For the operation of LEDs, it is in principle already known to use an operating circuit comprising switching regulators. For example, switching regulators such as buck converters or step-down converters, boost converters or step-up converters, flyback converters etc. can be used for driving LEDs. In this case, a control unit drives a clocked semiconductor power switch, by means of which, in the switched-on state of said semiconductor power switch, an inductance is magnetized, wherein, in the switched-off state of the switch, the inductance is then discharged or demagnetized via the LEDs, for example.
The switch can be controlled by the control unit via pulse width modulation (PWM). It is known in particular to use a constant radiofrequency frequency of the order of magnitude of, for example, 100 kHz for the PWM control signal. By selecting a corresponding duty cycle of the PWM control signal, dimming of the LEDs can then be made possible.
Furthermore, the use of operating circuits which support regulation of, for example, the power supplied to the LEDs or the current supplied to the LEDs is known for regulated operation of LEDs. Such regulation requires a fed-back measured variable, which can reproduce directly or indirectly, for example, the voltage drop across the LEDs and/or the current flowing through the LEDs.
In the case of regulation of the LED current, a regulator is used to attempt to keep the current through the LEDs constant. An operating circuit comprising such regulation should also be usable for different LED loads.
One problem with such regulation, however, consists in the fact that the regulation behavior can change depending on the LED load and depending on the dimming value, for example. One disadvantage here consists in the varying behavior of the regulator in respect of stability and temporal response, for example.
Therefore, the object of the present invention consists in providing an operating circuit for at least one light-emitting diode and a method for operating at least one light-emitting diode which improves the regulation of the current, voltage or electric power supplied to the LED even when different LED loads are connectable.